Color of chemicals
The color of chemicals is a
The study of chemical structure by means of energy absorption and release is generally referred to as spectroscopy.
Theory
All atoms and molecules are capable of absorbing and releasing energy in the form of photons, accompanied by a change of quantum state. The amount of energy absorbed or released is the difference between the energies of the two quantum states. There are various types of quantum state, including, for example, the rotational and vibrational states of a molecule. However the release of energy visible to the human eye, commonly referred to as visible light, spans the wavelengths approximately 380 nm to 760 nm, depending on the individual, and photons in this range usually accompany a change in atomic or molecular orbital quantum state. The perception of light is governed by three types of color receptors in the eye, which are sensitive to different ranges of wavelength within this band.
The relationship between energy and wavelength is determined by the
where E is the energy of the
The relationships between the energies of the various quantum states are treated by
Colors by wavelength
Below is a rough table of wavelengths, colors and complementary colors. This utilizes the scientific CMY and RGB color wheels rather than the traditional RYB color wheel.[1]
Wavelength (nm) |
Color | Complementary color | ||
---|---|---|---|---|
400–424 | Violet | Yellow | ||
424–491 | Blue | Orange | ||
491–570 | Green | Red | ||
570–585 | Yellow | Violet | ||
585–647 | Orange | Blue | ||
647–700 | Red | Green |
This can only be used as a very rough guide, for instance if a narrow range of wavelengths within the band 647-700 is absorbed, then the blue and green receptors will be fully stimulated, making cyan, and the red receptor will be partially stimulated, diluting the cyan to a greyish hue.
By category
The vast majority of simple inorganic (e.g.
Examples
Name | Formula | Color | |
---|---|---|---|
Alkaline earth metals
|
Mg2+ | Colorless | |
Scandium(III) | Sc3+ | Silver | |
Titanium(III) | Ti3+ | Purple | |
Titanium(IV) | Ti4+ | Silver | |
Titanyl | TiO2+ | Colorless | |
Vanadium(II) | V2+ | Light purple | |
Vanadium(III) | V3+ | Dark grey-green | |
Vanadyl(IV)
|
VO2+ | Blue | |
Vanadium(IV) (vanadite) | V 4O2− 9 |
Brown | |
Vanadium(V) (pervanadyl) | VO+ 2 |
Yellow | |
Metavanadate | VO− 3 |
Colorless | |
Orthovanadate
|
VO3− 4 |
Colorless | |
Chromium(II) | Cr2+ | Bright blue | |
Chromium(III) | Cr3+ | Blue-green-grey | |
Chromium(III) hydroxide | Cr(OH)63− | yellowish | |
Monochromate
|
CrO2− 4 |
Yellow | |
Dichromate
|
Cr 2O2− 7 |
Orange | |
Manganese(II) | Mn2+ | Pale pink | |
Manganese(III) | Mn3+ | Crimson | |
Manganate(V) | MnO3− 4 |
Deep blue | |
Manganate(VI) | MnO2− 4 |
Dark green | |
Manganate(VII) (permanganate) | MnO− 4 |
Deep purple | |
Iron(II) | Fe2+ | Greenish | |
Cobalt(II) fluoride | Co2+ | Pink | |
Cobalt(III) amine | Co(NH 3)3+ 6 |
Yellow/orange | |
Nickel(II) | Ni2+ | Light green | |
Nickel(II) amine complex | Ni(NH 3)2+ 6 |
Lavender/blue | |
Copper(I) amine complex | Cu(NH 3)+ 2 |
Colorless | |
Copper(II) | Cu2+ | Blue | |
Copper(II) amine complex | Cu(NH 3)2+ 4 |
Indigo-blue | |
Copper(II) chloride | CuCl2− 4 |
Blue - Green | |
Zinc(II) | Zn2+ | Colorless | |
Silver(I) | Ag+ | Colorless | |
Silver(III) in conc. HNO3 | Ag3+ | Dark brown |
It is important to note, however, that elemental colors will vary depending on what they are complexed with, often as well as their chemical state. An example with vanadium(III); VCl3 has a distinctive reddish hue, whilst V2O3 appears black.
Salts
Predicting the color of a compound can be extremely complicated. Some examples include:
- Cobalt chloride is pink or blue depending on the state of hydration (blue dry, pink with water) so it is used as a moisture indicator in silica gel.
- Zinc oxide is white, but at higher temperatures becomes yellow, returning to white as it cools.
Name | Formula of the corresponding salts |
Color | Picture |
---|---|---|---|
Iron(III) chloride hexahydrate
|
FeCl3·6H2O | Yellow/brown | |
Iron(III) chloride anhydrate | FeCl3 | Black | |
Chromium (III) sulfate
|
Cr2(SO4)3 | Dark green | |
Copper(II) sulfate anhydrate | CuSO4 | White | |
Copper(II) sulfate pentahydrate
|
CuSO4·5H2O | Blue | |
Copper(II) benzoate | Cu(C7H5O2)2 | Blue | |
Cobalt(II) chloride | CoCl2 | Deep blue | |
Cobalt(II) chloride hexahydrate
|
CoCl2·6H2O | Deep magenta | |
Manganese(II) chloride tetrahydrate | MnCl2·4H2O | Pink | |
Copper(II) chloride dihydrate | CuCl2·2H2O | Blue-green | |
Nickel(II) chloride hexahydrate | NiCl2·6H2O | Green | |
Lead(II) iodide | PbI2 | Yellow | |
Ammonium dichromate | (NH4)2Cr2O7 | Orange |
Ions in flame
Name | Formula | Color | |
---|---|---|---|
Lithium | Li | Red | |
Sodium | Na | Yellow/orange | |
Magnesium | Mg | Brilliant white | |
Potassium | K | Lilac/violet | |
Calcium | Ca | Brick red | |
Rubidium | Rb | Red-violet | |
Strontium | Sr | Red | |
Caesium | Cs | Light blue | |
Barium | Ba | Green/yellow | |
Copper | Cu | Blue/Green(Often with white flashes) | |
Lead | Pb | Grey/White |
Gases
Name | Formula | Color | |
---|---|---|---|
Hydrogen | H2 | colorless | |
Oxygen | O2 | pale blue | |
Ozone | O3 | pale blue | |
Fluorine | F2 | pale yellow | |
Chlorine | Cl2 | greenish yellow | |
Bromine | Br2 | red/brown | |
Iodine | I2 | dark purple | |
Chlorine dioxide | ClO2 | intense yellow | |
Dichlorine monoxide | Cl2O | brown/yellow | |
Nitrogen dioxide | NO2 | dark brown | |
Trifluoronitrosomethane | CF3NO | deep blue | |
Diazomethane | CH2N2 | yellow |
Bead tests
A variety of colors, often similar to the colors found in a
Metal[3] | Oxidizing flame |
Reducing flame
|
---|---|---|
Aluminum |
colorless (hot and cold), opaque | colorless, opaque |
Antimony | colorless, yellow or brown (hot) | gray and opaque |
Barium | colorless | |
Bismuth | colorless, yellow or brownish (hot) | gray and opaque |
Cadmium | colorless | gray and opaque |
Calcium | colorless | |
Cerium | red (hot) | colorless (hot and cold) |
Chromium | Dark yellow (hot), green (cold) | green (hot and cold) |
Cobalt | blue (hot and cold) | blue (hot and cold) |
Copper | green (hot), blue (cold) | red, opaque (cold), colorless (hot) |
Gold | golden (hot), silver (cold) | red (hot and cold) |
Iron | yellow or brownish red (hot and cold) | green (hot and cold) |
Lead | colorless, yellow or brownish (hot) | gray and opaque |
Magnesium | colorless | |
Manganese | violet (hot and cold) | colorless (hot and cold) |
Molybdenum | colorless | yellow or brown (hot) |
Nickel | brown, red (cold) | gray and opaque (cold) |
Silicon | colorless (hot and cold), opaque | colorless, opaque |
Silver | colorless | gray and opaque |
Strontium | colorless | |
Tin | colorless (hot and cold), opaque | colorless, opaque |
Titanium | colorless | yellow (hot), violet (cold) |
Tungsten | colorless | brown |
Uranium | Yellow or brownish (hot) | green |
Vanadium | colorless | green |
References
- ^ "SAP Fiori | SAP Community".
- ^ Flame Tests at chemguide.co.uk
- ISBN 0-8493-0466-0.